Blood-borne pathogens are a significant healthcare problem. A delayed or improper diagnosis of a bacterial infection can result in sepsis, a serious, and often deadly, inflammatory response to the infection. Sepsis is a leading cause of death in the United States. Early detection of bacterial infections in blood is the key to preventing the onset of sepsis. Traditional methods of detection and identification of blood-borne infection include blood culture and antibiotic susceptibility assays. Those methods typically require culturing cells, which can be expensive and can take as long as 72 hours. Often, septic shock will occur before cell culture results can be obtained.
Pathogens during active blood-borne infection or after antibiotic treatment are typically present in minute levels per mL of body fluid. Several techniques have been developed for isolation of pathogens in a body fluid sample, which include molecular detection methods, antigen detection methods, and metabolite detection methods. These conventional methods often require culturing specimens, such as performing an incubation or enrichment step, in order to detect the low levels of pathogens. The incubation/enrichment period is intended to allow for the growth of bacteria and an increase in bacterial cell numbers to more readily aid in isolation and identification. In many cases, a series of two or three separate incubations is needed to isolate the target bacteria. Moreover, enrichment steps require a significant amount of time (e.g., at least a few days to a week) and can potentially compromise test sensitivity by killing some of the cells sought to be measured.
To avoid incubation/enrichment periods and to reduce overall time, other techniques have been developed to rapidly isolate low levels of pathogens from body fluids. Those techniques often utilize antibody bound particles specific to a target pathogen and a sorting apparatus such as an affinity column or magnetic surface. Although successful at rapidly separating small amounts of pathogens from the bodily fluid, these techniques have multiple steps, such as binding targets to the particles, binding to target/particle complexes to a sorting apparatus, isolating bound target/particle complexes from the body fluid sample, in which a failure at any step can result in the inability to isolate pathogens that are present in the bodily fluid. That is, failure at any one step can result in a failed assay.
Currently, there is no effective way to distinguish between a successful assay that correctly identifies the absence of a pathogen and a failed assay in which a pathogen was present but just not isolated. Because the failure to detect and treat blood-borne pathogens can result in significant health problems, there is a need to develop a method for rapid isolation of pathogens from a sample, such as a blood sample, that indicates whether the assay properly isolated suspected pathogens.